In recent years, image reading apparatuses including a scanner are widely used with widespread use of personal computers. Among these apparatuses, a flatbed image reading apparatus has an advantage that it can read a thick original such as a book.
FIG. 11 is a cross-sectional view schematically showing the structure of a conventional flatbed image reading apparatus. In the image reading apparatus in FIG. 11, an original is placed face down on a platen glass 51 provided on an upper surface of apparatus main body 50. A contact image sensor 52 provided in the apparatus main body 50 scans the original while it is moved along the surface of the original, thus optically reads the image of the original.
In the image reading apparatus, a document cover 53 as an original pressing member is openably/closably attached to the apparatus main body 50 such that the original is brought into intimate contact with the platen glass 51.
The document cover 53 is rotatably attached to the apparatus main body by a hinge 54 provided at a rear end of the apparatus. A document press-fixing member 55 such as a sponge is attached to the platen glass side.
The original is placed on the platen glass 51 and the document cover 53 is closed, thereby the original is pressed against the platen glass 51 and is fixed on the platen glass 51.
The above-described conventional flatbed image reading apparatus requires space for placement equal to or greater than the size of the original. If the apparatus is designed to read a large-sized original, it requires large space for placement of the apparatus.
However, as the contact image sensor for image reading is very small and light-weighted, and the height of the apparatus main body 50 is not so great, the apparatus main body 50 may be set upright with its side down using a stand 56 as an accessory tool, as shown in FIGS. 12A and 12B.
The original which can be scanned in the upright state is limited to a sheet type original. If the apparatus is arranged such that the document cover 53 and the end of the apparatus main body 50 are brought into contact with each other by a suction cup or the like, the original can be scanned while it is pressed against the platen glass 51.
On the other hand, the document cover 53 in the conventional structure opens/closes by rotation on the hinge 54 as a rotational axis in the rear end, however, the document cover 53 cannot press a thick original such as a book in this structure. Generally, the hinge 54 is configured slidable in upward and downward directions when the apparatus main body 50 is placed in level, and the document cover 53 floats from the platen glass, so that the document cover 53 can press the thick original against the platen glass.
However, in the image reading apparatus which can be set upright, if the hinge 54 in the horizontal position is upward/downward slidable, the hinge 54 slides when the apparatus is set upright, the document cover 53 floats from the platen glass 51 and cannot press the original properly. Accordingly, the slide hinge cannot be employed, and the thick original cannot be scanned by this structure.
Further, FIG. 13 shows a two-step hinge type structure as another example where two hinge members A and B are provided between the document cover and the apparatus main body, and the hinge member B has an additional function of restoring the positional relation between the document cover and the apparatus main body so as to open the document cover. In this structure, the document cover does not open when the apparatus is set upright. Further, when the apparatus is set in level, a thick original can be pressed against the platen glass in a stable manner.
However, in the two-step hinge type image reading apparatus, especially when it is set upright, the constant positional relation cannot be properly maintained between the document cover and the platen glass when the document cover is closed, due to backlash of the rotational axis between the document cover and the hinge member in the axial direction.
Further, when the document cover of this two-step hinge type structure for a thick original is closed from an opened state, as the barycenter of the document cover is higher than the rotation axes of the two hinges, the rotational axis of the hinge A, not the rotational axis of the hinge B, becomes the rotational axis of the document cover. Especially, as shown in FIG. 13, if the rotational axis of the hinge B is out of a straight line passing through the barycenter of the document cover and the hinge A, there is torque to open the document cover about the hinge B when the document cover is open. Accordingly, the hinge B does not follow the movement of the document cover to close but it buckles as shown in FIG. 13. As a result, a user feels insecure about opening/closing operations, and further, if the end of the document cover is brought into contact with the original, the original may be damaged.
Further, when the apparatus is set upright, the opening/closing operations of the document cover are unstable due to a similar reason. Further, as the document cover is closed in a buckled state, a sufficient pressing force cannot be obtained to press the original against the platen glass. Accordingly, the original may float from the platen glass, and the quality of read image may be degraded.